I use both 2560x and 3440x ultrawides.
You definitely feel the lack of desktop space when moving back to 2560x1080p but it really depends on how you use windows. if you are heavy on multi tasking with windows side-by-side then 2560x1080 will hold you back. However, i use them both differently. I dont heavily multi task on my 2560x at home - most things i do are either full screen or split 70/30 with a video playing in one third of the screen, something like that. at work ive always got multiple windows open and the resolution increase is very much needed. at home, 3440x1440 is more of a want but then i'd need to buy a few hundred quids worth of extra gpu as well so...meh.